Tilting-type double hung windows allow the individual window sash to be tilted inward for purposes of cleaning. While this feature is extremely convenient, a window sash which can be tiltably disengaged from the window jamb may not be capable of withstanding wind loading normally encountered in high rise buildings.
The lock structures on double hung windows typically connect only the upper and lower window sash to each other, rather than to the window jamb. High wind loads may also cause the window jamb to partially separate from the window frames, allowing outside air into the building. Finally, the anti-tilting locks provided on tilting-type double hung windows provide only limited security against forced entry.
U.S. Pat. No. 4,521,991 issued to Sayer et al. on Jun. 11, 1985, discloses a locking member which is inserted between the window sash and the window jamb to provide additional structural strength to a tilting-type double hung window. The locking mechanism of Sayer requires a customized jamb liner and window sash structure to operate the locking mechanism. The elongated locking member must be removed from the channels between the window sash and the window jamb before the window sash can be tilted inward. During normal operations with the locking member in place, the window cannot be tilted inward. Finally, the locking member provides additional friction to opening and closing the window.